The invention relates to “active implantable medical devices” as defined by the Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implantable cardioverter defibrillators (ICDs), which are devices capable of applying an antitachycardia therapy by delivering defibrillation or cardioversion shocks, that is to say electric pulses of high energy, considerably exceeding the energy delivered by a myocardium stimulation.
These devices are generally implanted for primary prevention in patients with a particular clinical problem, typically patients who have had a heart attack with electrophysiological abnormalities, or coronary and/or heart failure patients with reduced ejection fraction. Specifically, the current recommendations for an indication of prophylactic implantation of a defibrillator are:                Patient with a coronary artery disease, without or with mild to moderate symptoms of heart failure and ejection fraction ≦30% measured at least one month after a heart attack, or        Patient with apparently primitive dilated cardiomyopathy, with ejection fraction ≦35% and symptoms of mild to moderate heart failure (NYHA class II or III).        
However, when examining afterwards the effective utilization rate (delivery of at least one therapy) of defibrillators that were implanted in patients using these criteria, it is shown that very few patients benefit from their defibrillator. In a 2005 study, it appears that 81% of patients have never been subjected to a defibrillator therapy over a period of 5 years.
The implantation of a defibrillator is not a trivial operation. Firstly, the defibrillator algorithms may wrongly detect ventricular tachycardia, leading to the delivery of unnecessary or deleterious shocks, affecting the quality of life of the patient. Beyond the inconvenience caused by this type of painful and distressing shock for the patient, it was also demonstrated that these inappropriate shocks increase the risk of death. Secondly, the defibrillation leads are fragile and complex devices, with a significantly higher failure rate than that of simple pacing leads. Patients implanted with an implantable defibrillator are therefore statistically more often the subject of reoperation than those with a simple pacemaker or resynchronizer. Thirdly, implanted defibrillators for primary prevention are often programmed to treat only the very high rate arrhythmias. In the area of “slow ventricular tachycardia” (“slow TV”), between 100 and 150 bpm, all therapies are disabled, this area being only used for monitoring the patient. However, the slow TV can be halted by alternative therapies to shock delivery, including therapies called “ATP” (AntiTachycardia Pacing) acting through a programmed stimulation at a frequency adapted for tachycardia, which would prevent the patient from worsening conditions.
One object of the invention is to overcome these difficulties by proposing a system for the evaluation and adaptation of antitachycardia therapy by shock delivery. This system includes an implantable defibrillator that can automatically evaluate the actual risks of deleterious ventricular arrhythmia in the patient, and automatically adapt its programming (modification of rhythm analysis algorithms, of the detection sensitivity, etc.) according to risk actually incurred by the patient, so as not to trigger an alarm and/or activate a potential shock therapy in the event of major arrhythmia risk. Otherwise, the shock therapy can be deactivated, thereby avoiding the delivery of inappropriate, painful, and harmful shocks, favoring a potential ATP therapy.
Most analysis techniques proposed so far to quantify the risk of developing malignant ventricular arrhythmia are based on the study of a single descriptor (univariate study): case of Non-Sustained Ventricular Tachycardia (NSVT), Heart Rate Variability (HRV), Heart Rate Turbulence (HRT), QRS width, QT length, etc.
For example, US 2011/0190650 A1 assesses the risk of sudden death based solely on the dispersion of the QT segment, a descriptor measured on ECG recordings and compared to a preset value. If the measured dispersion is significantly different from the preset value, the patient is considered at risk of sudden death, which justifies the prophylactic implantation of a defibrillator.
Multivariate studies were also conducted, for example to assess the T Wave Alternans combination (TWA)+late potentials, or the combination HRT+TWA+reduced ejection fraction. These multivariate studies, however, only evaluate linear combinations of descriptors, with specificity only slightly higher than what could be obtained with the other techniques.
WO 2009/088627 A1 is thus based on the comparison of descriptors obtained from Holter monitoring with predetermined values, the risk criterion being based on the number of descriptors beyond pre-established thresholds.
US 2011/0301479 A1 discloses calculating all Holter recording descriptors and dividing them into three categories, corresponding to the decomposition of the Coumel triangle (which will be explained below). In each of these three categories, the descriptors are compared to preset values considered “normal”, and for each category, a risk sub-criterion is established based on the ratio of the descriptors which are within the bounds of this “normality” and those who are outside these bounds. The final criterion of risk of sudden cardiac death is the ratio between the number of these three, validated or not, categorical risk sub-criteria.
U.S. Pat. No. 5,251,626 A describes a device for detection and treatment of arrhythmias implementing a neural network. This technique however has the drawback of making overall analysis of the various parameters used to trigger an arrhythmia, by averaging and mixing information from the various relevant arrhythmogenic criteria. The specificity of the device is thus relatively low, leading to a high proportion of false positives and false negatives.
These different techniques above are thus in practice not very discriminatory because they rely on too simple models (with single descriptor and/or based on threshold crossings) and do not reflect the reality of physiological phenomena, which involve a number of important nonlinearly interacting factors.